An LED diode (hereinafter, it is referred to “LED”) is used in lighting devices to satisfy requirements of low power consumption, high efficiency, and long lifetime.
In order to use an LED as a light source, a switching circuit to operate the LED according to an input voltage is necessary.
A conventional switching circuit includes a voltage sensing circuit or period sensing circuit to sense the amount of a voltage or an input period of a voltage, thereby controlling a switch corresponding to an LED. Since the conventional switching circuit includes the voltage sensing circuit or the period sensing circuit, its entire size is too big. Thus, the marginal area to include more LEDs is reduced.
In addition, the switching circuit is formed by a FET, and the FET IC is a sensitive component, and very weak to heat. Herein, when an input voltage equal to or greater than a rated voltage is inputted, a significant amount of heat may generate at the switching circuit. That is, when the input voltage equal to or equal to or greater than the rated voltage is inputted, current with high amperes flows through the switching circuit, thereby generating a significant amount of heat at the switching circuit.
In U.S. Pat. No. 6,989,807, in an AC (alternating current) input voltage having real time voltage change, LEDs are operated under the real time voltage change condition by controlling a plurality of switches connected in parallel to a plurality of the LEDs connected in series. However, since a voltage sensing circuit sensing the input voltage is included in U.S. Pat. No. 6,989,807, an area for mounting more LEDs decreases, and a significant amount of heat generates at the switching circuit when a voltage equal to or greater than the rated voltage is inputted, thereby increasing power consumption, reducing its efficiency, and increasing occurrence of malfunctions of the circuit due to the significant amount of heat generated at the switching circuit.